\foreach \i/\j in {0.5/$H_{0}$, 1.5/$H_{0}$ } {
        \node at (4.5, -\i) {\j};
    }
    \node[PR] at (3.48, -0.5) {};
         \node[PR] at (3.48, -1.5) {};
    \node[PR] at (3.48, -3.5) {};
        \node[PR] at (3.48, -1.5) {};
